A. Field of Invention
This invention relates to asphalt packaging, in particular, to an improved apparatus and method for packaging asphalt.
B. Related Art
The present invention constitutes an improvement over the invention described in the application Ser. No. 682,192, which involved packaged roofing asphalt and a method for making it.
The packaged roofing asphalt of the earlier invention comprised a molded block of solid asphalt contained in a flexible film consisting essentially of polypropylene and being the sole containment means for the block. The film has a melting point between about 275.degree. F. and about 335.degree. F. (for example, about 315.degree. F.) and a thickness between about 1.0 and 1.8 mils.
The method of the earlier invention involved the steps of providing a mold of a rigid material, lining the mold with a flexible film, pouring liquid roofing asphalt into the film-lined mold, cooling the mold to solidify the asphalt, and removing the solidified asphalt covered with the flexible film to provide an asphalt packaging. The roofing asphalt of the packaging is asphalt material typically used in roofing applications. Such materials have a melting point between about 170.degree. F. and 220.degree. F.
In the earlier invention, the flexible film is the sole containment means for the asphalt and consists essentially of polypropylene. It has been found that a flexible film of polypropylene which has the particular thickness and particular melting point recited above has the proper balance of strength for containing the liquid asphalt during the packaging operation and meltability to allow it to melt quickly and completely in a roofing asphalt vat used in the conventional manner.
In the prior invention, asphalt 101 is formed into a block, and is covered by polypropylene film 103. The asphalt 101 need not be completely covered by the film 101, but molding techniques usually required to form the package of the invention would generally require that the bottom and the four sides be covered. The package is dimensioned to be convenient for storage, handling and insertion into a roofers asphalt vat. A preferred size is 22 inches long, 11 inches wide, and 6 inches high, resulting in a package with 50 pounds of asphalt. This size permits easy handling, and can be easily stacked for storage and shipping with little void space. FIG. 7 shows the stacking of packages 101 on a conventional shipping pallet 107. Referring to FIG. 7, the packaging may have a portion of the top surface 105 uncovered by the film to expose a surface of asphalt. Preferably more than 3/4 of the top surface is covered by the polypropylene film 103. For the above 22.times.11.times.6 package the exposed portion is about 1 .TM..times.14 inches. When such packages are stacked on a pallet, the top asphalt surface of a package will adhere to the bottom of an adjacent package, stabilizing the stack. However, packages 101 may still be easily separated and removed when unstacked. The preferred size of the package also allows insertion of the whole package into an asphalt vat without having to cut or chop the package into small pieces. Its dimensions also allow the package to melt quickly in the vat. Since the film is not removed before inserting the package to the vat, there is no packaging waste and cleanup. The thin-walled polypropylene film material quickly melts with the asphalt and leaves no solid or partially melted residue in the asphalt melt.
The previous invention provided a general manufacturing procedure, which included the steps of providing a rigid, heat resistant mold, lining the mold with a polypropylene film and pouring liquid asphalt into the lined mold. Such a mold 401 is illustrated in FIGS. 8A and 8B. The polypropylene film 403 is inserted in the mold 401 as shown in FIG. 8B, to line the mold 401 with polypropylene film 403. The mold 401 may be of any suitable material. Plastics, cellulosic materials, and the like may be used if the mold is to be used once or only a few times. For more durable molds, a heat resistant plastic material, or preferably sheet or cast metal, is used.
The polypropylene film 403 has the melting point and thickness recited above. Higher melting point and thicker materials do not completely melt in the asphalt vat, while lower melting point and thinner materials do not have the strength required for the manufacture of the packaging. The polypropylene film 403 may be in the form of a sheet or in the form of a bag, preferably dimensioned to be easily inserted into the mold 40 and also to cover all the surfaces of the mold to prevent the asphalt from adhering to the mold 401.
Asphalt in a liquid form is poured into the mold. FIG. 9 is a cross-section showing mold 501, film 502 lining the mold, and asphalt 505 being poured into the mold 501. The asphalt is poured at a temperature between about 280.degree. F. and 310.degree. F. Below this temperature range the asphalt is too viscous, and above this it may damage the film. The optimum temperature range is about 295.degree. F.
After pouring the asphalt into the mold, the portion of the polypropylene film extending above the sides of the mold is folded over the top of the liquid asphalt. Preferably, the portion of the film folded over the top is sized to not completely cover the top of the package and leave an exposed surface of asphalt. In the prior invention, the resulting package will have a top surface with the asphalt partially exposed.
The earlier invention provided cooling means, e.g. a water bath, a jacketed mold, or the like, to accelerate the cooling of the asphalt in the mold. The earlier invention provided a trough containing water, with the molds placed in the trough to cool the molds. The molds with the melted asphalt were charged into one end of the trough and moved though the trough, e.g. by floating the molds or by a conveyor means, while the water cooled the outer surface of the molds. The cooled molds with the solid asphalt were then discharged from the other end of the trough. When the asphalt was sufficiently cool to be solid, the asphalt covered by the polypropylene film was removed from the mold.
U.S. Pat. No. 3,837,778 to Parker also refers to a packaging method utilizing water troughs. That patent states that hot asphalt is poured into a mold or boat that is lined by polyester film at a charging station, such boat being floated on a stream of cooling water that carries the boat and its cooling contents to a discharge station where the cooled asphalt enveloped in the resin film is removed from the boat as the packaged product with the boat being returned to the charging station for reuse.
One of the shortcomings of these prior systems is their elaborate and complicated construction. In contrast, the present invention offers a far more effective and less expensive system. Further, the present invention presents less potential for mechanical difficulties and greater ease of construction and maintenance than prior systems.